Project Summary There is an epidemic of chronic kidney disease (CKD) in Central America, and the prevalence has been increasing over the past 20 years. El Salvador has the highest overall mortality rate from kidney disease in the world, and CKD is the second leading cause of mortality among men of working age. Due to its unique characteristics, the disease is referred to as Mesoamerican Nephropathy (MeN). In the US and Europe, CKD is common in older populations (age>60), affects men and women equally, and is primarily due to diabetes and hypertension. In contrast, CKD in certain regions of Central America disproportionately affects younger men and appears to be unrelated to diabetes or hypertension. Agricultural workers are the most affected, but the specific cause(s) remains unknown. The goal of the parent research is to investigate the potential roles of exposure to the herbicide glyphosate, heavy metals and heat stress on the risk of MeN among agricultural workers in El Salvador. The study aims to determine whether glyphosate, heat stress and/or nephrotoxic metals, alone or in combination, cause kidney injury. We will also investigate whether biomarkers of kidney injury lead to decreased kidney function over time. Results of the study may contribute to occupational and environmental heath interventions related to these three exposures, as well as contribute to the understanding of kidney injury biomarkers, which may be used for early detection and treatment to mitigate kidney injury and CKD risk. Results may also inform other CKD epidemics with similar characteristics that have been described in our countries including India and Sri Lanka. Our aims are: (1) Recruit and establish a cohort of 300 workers in El Salvador; (2) Measure heat, conduct physical examinations of workers, and collect urine and blood samples to characterize exposure to metals and glyphosate at baseline, biomarkers of kidney injury, and exposure to heat stress and muscle damage, pre- and post-shift over three consecutive workdays; (3) Investigate industry, job task, duration of employment, metals, glyphosate and heat stress, as predictors of kidney function (eGFR) over a 30-month period; (4) Bank biological samples for future analysis of additional hypotheses as they emerge; and (5) Communicate individual kidney function results to cohort participants, and overall study results to cohort participants, the scientific community, public health officials and the general public. The proposed analyses in this supplement will serve two purposes: 1) Provide us with the most reliable measures of glyphosate available using the gold-standard method, and allow for comparison of glyphosate concentrations with other cohort studies using the same methods, and 2) Provide an additional and widely considered more reliable measure of kidney function, our primary outcome, based on analyses of serum cystatin-c.